1. Field of Disclosure
The present disclosure of invention relates to an apparatus and a method for synchronizing a roll-to-roll transfer device. More particularly, the present disclosure of invention relates to an apparatus and a method for synchronizing a roll-to-roll transfer device capable of preventing a failure or a damage of a nano thin-film in transferring the nano thin-film using a synchronizing device via a roll-to-roll feeding process.
2. Description of Related Technology
In the conventional semiconductor process for manufacturing an electronic device, a substrate used in the process is limited because of the manufacturing process requiring high temperature. Thus, a nano thin-film roll transfer process, in which a nano thin-film device manufactured in the semiconductor process is detached from a rigid substrate and then is transferred to a flexible substrate, has attracted great interest in the field of flexible electronics. This transfer process is called by a plate to roll (P2R) transfer technique; the plate is typically a wafer with thin film devices, and the roll is the stamp for picking the thin film devices and for placing them on a polymeric film.
However, in the above-mentioned P2R transfer process, the size of the thin-film is limited by the size of the wafer or a rigid substrate endurable for high temperature process. To overcome this size limitation and increase the productivity, a continuous transfer process is required. One of the methods for continuously transferring the nano thin-film is the roll-to-roll process. In the roll-to-roll process, the nano thin-film is disposed between a pair of rollers and the rollers continuously make contact between the nano thin-film and a continuous film of polymer.
In a roll-to-roll transfer device, a contact surface between the roller and the nano thin-film should be precisely controlled because a cylindrical roller is used and thus the roller and the nano thin-film make continuous contact with each other. Without the precise control, as illustrated in FIG. 1, creases A1 or cracks A2 occur in the nano thin-film and thus the electrical or mechanical quality of the transferred thin film degrades.
In the transfer process, the creases or cracks may be caused by deformation of the roller or irregular load of the roller due to the contact between the roller and the nano thin-film or between the pairs of rollers.
A vertical load on the roll stamp can be controlled to decrease the creases or cracks of the nano thin-film in the transfer process. The creases or cracks can also occur when a horizontal load is applied to the nano thin-film, and thus the horizontal load should be controlled or minimized together with the vertical load. To minimize the horizontal load, linear velocities on surfaces of the pair of contacted rollers should be synchronized during the rotation of the rollers.
For example, when one of the rollers rotates faster than the other, the horizontal load is ununiformly applied to the nano thin-film and thus the creases or cracks may occur. Even though the rotational velocities of the pair of rollers are uniformly controlled, lengths of circumferences of the paired rollers and may be different with each other due to the machining uncertainty or the wear of the rollers, and thus the linear velocity of the paired rollers may also be different with each other.
When the nano thin-film is damaged during the roll-to-roll transfer process, the performance of the nano thin-film device may degrade.
Accordingly, the transfer of the nano thin-film should be monitored, the rotational velocities of the pair of rollers should be individually controlled, and thus the horizontal load induced by the difference of the linear velocities of the paired rollers should be minimized.
Related prior art is Korean laid-open application No. 10-2012-0044825.